Air cushion vehicle having lift fans

ABSTRACT

Air-cushion vehicle comprising one or more variable-pitch, axial flow, ducted lift fans, the pitch variation of which is controlled in dependence of the cushion pressure, attitude, lift power requirements or other conditions of operation of the vehicle.

United States Patent Inventor Andre Grihangne 186, Avenue Victor Hugo, 75-Plris, France Appl No. 778,712 Filed Nov. 25, 1968 Patented July 6, 1971 Priority Nov. 29, 1967 France 130,270

AIR CUSHION VEHICLE HAVING LIFT FANS 1 Chill, 6 Drawing Figs.

Int. Cl. B60v I/06 Field oISearch ISO/118, 120, 121, 117

[56] References Cited UNITED STATES PATENTS 3,174,573 3/1965 Chaplin 180/121 3,219,134 11/1965 Brattetal.... 180/121 3,373,836 3/1968 Chaplin 180/118 3,419,106 12/1968 Lawrence et al. 180/119 3,420,329 l/1969 Moore 180/118 3,467,213 9/1969 Walker 180/120 Primary Examiner-A. Harry Levy Attorney-Stevens, Davis, Miller & Mosher ABSTRACT: Air-cushion vehicle comprising one or more variable-pitch, axial flow, ducted lift fans, the pitch variation of which is controlled in dependence of the cushion pressure, attitude, lift power requirements or other conditions of operation of the vehicle.

PATENTED JUL 6197! SHEET 2 OF 4 FIG.

AIR CUSHION VEHICLE IIAVING LIFT FANS This invention relates to an air cushion vehicle or groundeffect machine having a structure which is lifted by at least one pressure-fluid cushion produced by one or more fans. It relates more particularly to the control of such fans in order to improve operating, stability and maneuverability conditions of the vehicle and extend its field of use.

According to the invention,'the lift cushion is fed by one or more variable-pitch axial ducted fans, the term variable pitch" meaning that the blades have a pitch angle which is adjustable either simultaneously for all the blades or cyclically in turn, the pitch control being elTected manually or automatically in dependence on the static or dynamic conditions of the vehicle.

In one embodiment of the invention, the hover-height and attitude stability of a ground effect machine lifted by a plurality of pressure fluid cushions each having its own supply fan, is controlled by varying the general pitch of one or other of the fans depending upon the instantaneous pressure in the cushion concerned or depending upon the instantaneous attitude of the machine suitably detected by a pendulum or another roll and pitch detector, e.g. gyroscopes.

If, instead of using one supply fan per cushion, a common fan is used for the simultaneous and independent supply of a plurality of cushions, as described more particularly in US. application Ser. No. 498,432 now US. Pat. No. 3,536,l55, then according to one feature of this invention it is advantageous to control the stability of the craft by cyclic variation of the pitch of the blades of the said common fan in order to provide a preferential supply to one or more of the said cushions, such cyclic pitch variation being additional to the general pitch variation if required.

The use of cyclic pitch variation is also advantageous in the case of a machine with a single cushion divisible into compartments by means of a stability skirt.

In the accompanying drawings,

FIG. I is a perspective and partly broken-away view of a variable pitch propeller system of known type used more particularly in aeronautics and suitable for the lift fans according to the invention.

FIG. 2 is a similar view of a fan system comprising general pitch and cyclic pitch variation, again of known type.

FIG. 3 is a diagrammatic axial section-of a fan and cushion unit mounted on a ground effect machine according to the invention.

FIG. 3A diagrammatically shows an embodiment of a differential general pitch control system for a machine comprising a plurality of units ofthe type shown in FIG. 3.

FIG. 4 is a similar view of an alternative embodiment comprising a common fan feeding a plurality of cushions, being a section on the line lV-IV in FIG. 5.

FIG. 5 is a diagrammatic top plan view of the same embodi ment.

Since the variable-pitch propeller system shown in FIG. I is known, it will not be described in detail hereinafter. It will simply be pointed out that the order given by the pilot at the control stick is transmitted to a slide valve 1 of a hydraulic or pneumatic distributor by means of an electrical, mechanical or other control 2. Movement of the valve causes a doubleacting hydraulic jack 3 to be fed by a hydraulic pump 4 supplied by an oil tank 25 incorporated in the hub and therefore movement of a piston 5 which is movable in parallel relationship to the axis of the rotating hub 6. The piston movements are transmitted via a rotary plate 7 integral therewith to levers 8 which control the pitch of each blade 9 which is mounted pivotally on the hub 6, which is rotated by the drive shaft I0.

The system for controlling the adjustment of the blades 9 is enclosed in a fixed casing or propeller cap II borne by supporting arms 12.

Of course a similar pitch control system will be provided for each fan if the vehicle has a plurality thereof.

Stroke-limiting stops corresponding to a maximum pitch will be provided on the hydraulic pistons 5 and adjusted according to the maximum torque permissible on the hub drive transmission shafts 10.

The cyclic pitch control may be carried out in known manner, for example as used on a helicopter and illustrated in FIG. 2, i.e. by means of two plates, arotating'pla te 26 connected to the hub by a caliper 27 and a stationary plate 28 held in place by a caliper 29 on the plate support 30, cyclic pitch variations being obtained by inclination of the plates about a swivel joint 31, the cyclic pitch being produced by the left and right lateral and longitudinal controls 32, 33, 34 and the general pitch being produced by means of a controller (not shown) on the structure.

Of course the above-described control systems could be replaced by other known systems allowing the pitch to be varied simultaneously or cyclically.

Referring to FIG. 3, reference 13 denotes the platform of a ground-effect machine, beneath which is secured a skirt l4 laterally bounding a plenumchamber 15 in which the lift cushion forms. The compressed air required for this purpose is delivered by a variable pitch fan l6 housed in a tunnel l7 and rotated by a drive shaft 18 through a bevel gear 19. The fan 16 has its axis vertical and draws atmospheric air in througha top aperture 20 and delivers it into the cushion 15 via a bottom aperture 2] formed in the platform I3.

The pitch of the fan 16 is changed by means of a servomotor 22 which is controlled either manually by the pilot or automatically, e.g. under the control of a pressure detector 23 situated at a suitably selected point of the cushion 15.

The machine may comprise a plurality of cushions like the cushion 15 for lifting purposes and an equal number of in' dividual variable-pitch supply fans like the fan 16. The fan drives may advantageously be synchronized in known manner by the provision of a combined transmission for the respective shafts 18. The pitch control, however, will remain separate for each fan.

FIG. 3A shows an embodiment of a pitch control system for two or more fans, using a hydraulic servomotor 22, operation being effected from the control stick 4].

By means of this stick, the pilot can change the general pitch of any one of the fans or a plurality thereof simultaneously as he wishes. The displacement of a rocker plate 42 controlled by the stick 41 acts on induction coils 43 which feed corresponding signals to an electronic amplifier 44. The latter controls a solenoid valve 45 which distributes oil under pressure to the double-acting jack 22, said oil originating from a pressurized tank 46 and causing the piston 22A to move in either direction. The said piston transmits its movement to the pitch control plate 47 of the fan 16.

It will be seen that the connection between the induction coil 43 and the amplifier 44 is made via a switch 48 which opens when piston 22A passes a given position.

of course, instead of being produced manually by the stick 41, the control signals fed to the solenoid valve 45 could be applied automatically, for example by means of the cushion pressure detector 23 shown in FIG. 3.

In this way, the stability of the machine can be controlled by controlling the pitch of each fan 16 by its control system 22 in accordance with the cushion pressure detected at 23 or any other parameter. If, for some reason, the cushion pressure changes, the detector 23 will either transmit this information to the pilot, who will then operate the stick 41, or will act automatically and directly on the servocontrol 22, thus changing the pitch of the blades of the fan 16 and hence the rate of airflow and delivery pressure so as to counterbalance the initial pressure variation of the cushion.

The use of a separate control 22 for each variable-pitch fan I6 enables the following operations to be carried out:

Control of rolling and pitch by production of different pressures in each of the skirts I4.

Restoration of zero attitude when the machine is exposed to wind.

Compensation of dig-in."

Restoration of zero attitude for fullv speed navigation (reduction of induced wave drag).

Roll inclination of machine by differentiation between the skirt pressures on each side in order to obtain an increased airflow on one side and a hydrodynamic increase on the other side, thus inducing two reactions which allow the following:

Control of side slip at low speed and yaw control at high speed (zero side slip).

Silent operations for coming alongside without the use of propellers.

Forward inclination of the machine in order to induce a rearward reaction to allow low speed navigation without using the propulsion system, thus giving low consumption and considerable independence for some operations.

Arrangement of a roll and pitch stabilizer system for the machine when stationary and under propulsion, from signals detected by a damped vertical control pendulum, said signals being amplified and corrected and then fed to the scrvomotor control system actuating the fan blade pitch.

Instead of having one fan per cushion as in the previous case, a plurality of cushions can be fed simultaneously and independently from a common fan, the supply being effected independently as described in the patent application cited hereinbefore.

FIGS. 4 and 5 show an arrangement of this kind with four juxtaposed cushions per fan. The latter will be of the type having a cyclically variable pitch, in the same way as helicopter rotors. By cyclically variable pitch" it is meant that the pitch of every blade varies in the course of each. revolution as a function of its instantaneous angular position. In other words, the blades have, at a given instant, different pitches and conversely each blade has a same pitch every time it passes through a given angular position. Of course, the platform 13 may be provided with a plurality of units like the one shown in FIGS. 4 and 5. I I

The same operations as before will be possible 'by a suitable selection of the cyclic variation of the pitch of the blades of the fan 16, one or more cushions receiving a preferential supply in relation to one or more other cushions.

lclaim:

1. In a vehicle borne on juxtaposed nonaligned air cushions clustered in a symmetrical distribution about a substantially vertical axis and supplied simultaneously though discretely with compressed air from successive sectors of the discharge of a same ducted fan centered on said axis adjacent said cushions and having variable-pitch rotor blades, a method of controlling the attitude of said vehicle in level condition, comprising the step of cyclically varying the pitch of said rotor blades relative to each other in every revolution thereof, whereby the air supply to one of said cushions is relatively enhanced at the expense of the air supply to another of said cushions. 

1. In a vehicle borne on juxtaposed nonaligned air cushions clustered in a symmetrical distribution about a substantially vertical axis and supplied simultaneously though discretely with compressed air from successive sectors of the discharge of a same ducted fan centered on said axis adjacent said cushions and having variable-pitch rotor blades, a method of controlling the attitude of said vehicle in level condition, comprising the step of cyclically varying the pitch of said rotor blades relative to each other in every revolution thereof, whereby the air supply to one of said cushions is relatively enhanced at the expense of the air supply to another of said cushions. 